Lithium sulfide is used, for example, as a raw material for a sulfide solid electrolyte which is one type of electrolytes used in a lithium ion secondary battery.
Conventionally, as a method of synthesizing lithium sulfide, a method of reacting hydrogen sulfide with Li2CO3 or Li2SO4 is known (Patent Documents 1 to 3).
In addition, as a method for synthesizing lithium sulfide using LiOH as a raw material, a method in which a solvent or an aqueous solution is used (Patent Documents 4 to 6) and a method in which hydrogen sulfide is reacted with LiOH in the absence of a solvent (Patent Document 7) are known.